Effect of repeated salt fog-dry cycles on the performances reversibility of flax fiber reinforced composites

This paper aims to evaluate the effectiveness of flax fiber reinforced epoxy composites (FFRCs) under realistic environmental conditions, contributing to the development of sustainable composite materials for semi-structural outdoor applications. For this purpose, the reversibility of FFRC performance under consecutive and repeated humid-dry aging cycles was investigated for the first time. In particular, FFRCs were exposed to three cycles (total aging time of 12 weeks), with each cycle (duration 4 weeks) comprising 10 days of wetting (salt-fog spray; 35 °C, 95 % RH, 5 wt% NaCl solution) and 18 days of drying (22 °C, 50 % RH). Three-point bending tests were carried out up to 18 days of drying within each cycle to monitor changes in the mechanical performances of composites. Water absorption capacity, density and void content were also assessed by tracking weight changes throughout the aging campaign. The experimental results highlighted that the humid phase of each cycle causes degradation of FFRC materials, even though they are able to fully recover their flexural strength during each dry phase, indicating reversible aging. On the other hand, a stiffness permanent reduction was observed due to irreversible degradation phenomena.